@Norman Hartnell
My anger comes from the sheer inefficiency of supporting more languages than are really needed in the world, and resuscitating ones that are dying just beggars belief. We need to move towards fewer languages to improve communication, not more. (I have this argument with my wife, whose native language is even less useful than Welsh, but not often - have you ever tried telling a Czech that the country's founders would have been better off sticking with German* instead of forcibly re-introducing a language that few people other than the nationalist academics spoke?)
However, I am honest enough to admit to myself that part of it is that many of these zombie languages are a) politically motivated, and when it comes to Welsh especially I don't see any justification for it, and b) they are often totally lacking in aesthetic appeal (Czech is awful, and Welsh and the other Gaelic languages aren't much better). Someone else used the term "spittle-flecked", and it sums it up nicely for me - if a language sounds like you are hawking up a mouthful of spit, then I hear someone doing just that, and it is offensive to me.
*Remember the modern Czech Republic/Czechoslovakia derives from the Austro-Hungarian empire, and the official language was German until about 1922, so I'm not referring to WW2.